This invention is related to electrical conductivity measuring devices, and in particular to conductivity measurement of fluids.
Industrial control systems and oceanographic studies frequently require the measurement of the electrical conductivity of a fluid, such as seawater. Several different types of conductivity sensors and systems have been developed to meet these requirements. The physical design of sensors for such measurements has proved to be challenging. Especially in ocean environments, the conditions that are present result in inevitable fouling of the sensor. Under extreme conditions, sensors may become so inaccurate or inoperable that they need to be replaced. Accordingly, a sensor design which minimizes the effects of such fouling on the accuracy of the measurement is very important.
The sensitivity, or calibration factor for conventional conductivity sensors is affected by the presence of nearby objects. Therefore, it may be necessary to calibrate them in the configuration in which they will be deployed, for example a deep-ocean sensor would have to be calibrated while mounted on the large pressure housing to which it is attached. This makes the calibration much more burdensome and interferes with easy replacement of malfunctioning sensors in the field.
The present invention includes a unique conductivity sensor configuration which has essentially no external electrical field. As a result, the calibration of the sensor is not affected by the existence of nearby external objects. Additionally, the sensor is relatively insensitive to electrode fouling or electrode polarization.
The sensor includes a tube through which the liquid to be measured may flow. An inner electrode plate extends partially along the length of the tube dividing the central portion of the tube into two sections. Two inner electrodes are located in the middle of the inner wall, one on each side, and two outer electrodes are located on the inside of the tube directly opposite the inner electrodes.
The electrode plate extends downwardly through a slot in the tube and further through a mounting base section. The base may be secured in a pressure housing, with the sensor being supported above the housing by the electrode plate. Conductive stripes on the surface of the electrode plate provide for electrical connection from within the housing to the inner and outer electrodes. Except for the electrodes, the conductive stripes are insulated from the conductive fluid, such as by an insulating coating applied over the stripes.